You're describing a non-issue. Simply use MySQLi instead of MySQL and you'll be able to install and use the board. Even 3.1.x should partially work with PHP 7. You will however encounter some issues, especially when it comes to custom BBCodes.

The fact that you're describing a standard setup issue caused by the transition to PHP 7 as a major issue with phpBB is just exaggeration.
phpBB 3.1.x requires PHP 5.3.3+ and therefore also supports the MySQL extension. The same applies to phpBB 3.2.x which has a minimum version of PHP 5.4.0.

Now let's please try to stop arguing about non-issues. Please only discuss phpBB 3.2.0-b2 in this topic.

The fact that you're describing a standard setup issue caused by the transition to PHP 7 as a major issue with phpBB is just exaggeration.
phpBB 3.1.x requires PHP 5.3.3+ and therefore also supports the MySQL extension. The same applies to phpBB 3.2.x which has a minimum version of PHP 5.4.0.

Now let's please try to stop arguing about non-issues. Please only discuss phpBB 3.2.0-b2 in this topic.

Please don't misunderstand me I appreciate the work of PHPBB developers team.
But for example my hosting provider OVH doesn't support php 5.3 anymore since march 2015.
So I would love that phpbb would be more oriented to the future than to the past

The fact that you're describing a standard setup issue caused by the transition to PHP 7 as a major issue with phpBB is just exaggeration.
phpBB 3.1.x requires PHP 5.3.3+ and therefore also supports the MySQL extension. The same applies to phpBB 3.2.x which has a minimum version of PHP 5.4.0.

Now let's please try to stop arguing about non-issues. Please only discuss phpBB 3.2.0-b2 in this topic.

Please don't misunderstand me I appreciate the work of PHPBB developers team.
But for example my hosting provider OVH doesn't support php 5.3 anymore since march 2015.
So I would love that phpbb would be more oriented to the future than to the past

At lot of other hosters are still at rather old PHP versions. Also, please note that supporting the MySQL extension in addition to the MySQLi one does not add any extra overhead both for your board and regarding the development. There is simply no point in intentionally not supporting the MySQL extension in PHP versions prior to 7.0. Hence why this is a non-issue.